1. Field of the Invention
This disclosure relates to a backlight unit, and more particularly, to a backlight unit adapted to improve uneven brightness and reliability, as well as a liquid crystal display device having the same.
2. Discussion of the Related Art
The fields to which liquid crystal display (LCD) devices are being applied are growing because of desirable features such as light weight, slimness, and a low driving voltage. This trend is confirmed in the ways in which the LCD devices have been applied to office automation equipment, audio equipment, video equipment, and so on. An LCD device controls the amount of light being transmitted on the basis of image signals applied to a plurality of control switches, in order to display a picture.
The LCD device, which is not self-luminescent, includes a backlight unit irradiating light on the rear surface of an LCD panel on which a picture is displayed. The backlight unit is classified as either of an edge type or a direct type in accordance with the placement of its light source.
Edge type backlight units have been applied to small and medium sized LCD devices. An edge type backlight unit includes a light source which is positioned at one its edges and a light guide panel guiding the light to be irradiated to the entire surface of the LCD panel.
On the other hand, direct type backlight units have been applied to larger LCD devices namely those above 12 inches. A direct type backlight unit includes a plurality of light sources arranged opposite the rear surface of the LCD panel. These plural light sources directly apply light to the rear surface of the LCD panel.
Electro-luminescent lamps (ELs), Cold cathode fluorescent lamps (CCFLs), hot cathode fluorescent lamps (HCFLs), or light emitting diodes (LEDs) are used as the light source of a general backlight unit. Among these light sources, LEDs have such as slimness, superior color reproduction, and low power consumption. The other light sources (i.e., the lamps) are configured to include a noxious heavy metal like mercury. As such LEDs have recently been increasingly used compared with other light sources.
The LED used in a related art backlight unit generates high heat. Due to this, the LED is loaded on a metal printed-circuit-board (PCB). Actually, an edge type backlight unit of the related art includes a metal PCB loaded with the LEDs. The metal PCB is fastened to one inner edge of a bottom cover of the edge type backlight unit by an adhesive.
However, in the edge type backlight unit of the related art, the metal PCB is separated from the bottom cover by heat generated when the LEDs are driven, thereby causing a misalignment of the LEDs. Accordingly, light leakage, a lack of uniform brightness, and other defects can be generated.
In addition, the edge type backlight of the related art can cause a light guide plate disposed parallel to the LEDs to be damaged by the separation of the metal PCB. As such, a malfunction occurs in the LCD device.